Recently, an all-digital phase-locked loop (ADPLL) circuit, where all control signals in a phase-locked loop (PLL) circuit are digitalized, has been used as a local oscillator in wireless communication devices, etc. In such a local oscillator, multiplying a frequency of a reference signal by a frequency multiplier and operating the PLL with the multiplied reference signal allows for setting a wider loop band. This allows for mitigating phase noise.
However, in general, since a duty ratio of the reference signal is not 50%, the multiplied reference signal includes a phase offset. Therefore, the multiplied reference signal disadvantageously includes frequency components of the reference signal. Due to this, spurs corresponding to the frequency of the reference signal are generated in the vicinity of an oscillating frequency. It is desired that such spurs be reduced.